1. Field of the Invention
The present invention relates to lighting fixtures for indirect room illumination through reflection of most of the fixture's light off of the room's ceiling, but also having a small, aesthetically pleasing downward component. More particularly, this invention relates to indirect office environment fluorescent tube lighting fixtures which are mountable close to the ceiling while providing uniform illumination of the ceiling and a high efficiency fixture.
2. Description of Prior Art
With the recent proliferation of Video Display Terminals (VDTs) in the office environment, lighting designers have identified high contrast overhead lighting as a source of glare and reflection on VDT screens. Such glare and reflection is an undesirable effect which impacts worker comfort and productivity. Thus, the need has arisen for efficient low contrast illumination of the work environment.
Indirect fluorescent tube overhead lighting has been determined to be the most efficient means of illuminating a large office environment, while providing low contrast illumination of the work area. Such lighting is accomplished by positioning fluorescent tube fixtures below the plane of the ceiling and directing nearly all of the light upward toward the ceiling. The light is then reflected off of the ceiling downward toward the room. However, low contrast illumination of the work area requires a uniform illumination of the ceiling.
Indirect fluorescent tube overhead lighting fixtures of the current art often must be suspended a significant distance below the plane of the ceiling in order to obtain a uniform light pattern. This phenomena is due to the fact that the optical reflector systems, or the lack thereof, in such fixtures distribute light output toward the ceiling at high angles (angles greater than 105 degrees from nadir) primarily directly above the fixture. Thus, the rows of such fixtures must be located close to one another, increasing the number and cost of the installation, or suspended farther from the ceiling in order to achieve uniform illumination of the ceiling. A problem, however, with mounting the fixtures a significant distance below the ceiling is that a ‘false ceiling’ impression is created by the rows of fixtures needed to illuminate a large work area. For instance, when looking out across a room containing multiple rows of suspended fixtures, the rows of fixtures themselves form a plane of fixtures at the suspension distance below the plane of the ceiling. In a room with 9 or 10 foot ceilings, a suspension distance of 24 to 36 inches will create an uncomfortably low false ceiling.
Previous efforts to design fixtures with lower angles of light distribution have resulted in less efficient fixtures.
Additionally, designers have found that eliminating glare does not in itself result in a pleasant environment. An appropriate perceived brightness has been found to be necessary to create comfort and a sense of well-being. Thus, lighting designers have recently indicated an preference for aesthetic, low illumination of the fixture housing when viewed from the working area of the room. However, efforts to design fixtures having illuminated housings when viewed from below have also resulted in less efficient fixtures.